1. Field of the Invention
The present invention relates to a blood pump for transferring blood. More specifically, this invention relates to a turbo blood pump in which centrifugal force generated by rotation of an impeller causes blood to flow.
2. Related Background Art
Blood pumps are indispensable to an artificial heart lung apparatus or the like for extracorporeal blood circulation. Among blood pumps, turbo blood pumps have been dominant. A turbo blood pump has a structure that is described as follows: a housing in which a pump chamber is formed includes an inlet port for introducing blood in a center portion and an outlet port for discharging blood in an outer peripheral portion; an impeller is disposed in the pump chamber, and rotation of the impeller causes blood to flow.
FIG. 5 shows a turbo blood pump as an example that is currently under development by the inventors of the present invention. In FIG. 5, a reference numeral 21 denotes a housing that includes an inlet port 21a and an outlet port (not shown). In the housing 21, a pump chamber 22 is formed and an impeller 23 is provided. The impeller 23 is supported rotatably by an upper bearing 24 and a lower bearing 25. In a concave portion 21b provided in a lower center of the housing 21, a rotor 26 is provided. Although not shown in the figure, the rotor 26 is connected to a motor and driven to rotate by the motor. In a lower and outer portion of the impeller 23, driven magnets 27 are provided in such a manner as to be positioned on an inner side of a side wall of the concave portion 21b of the housing 21. The rotor 26 is provided with driving magnets 28 in such a manner that the driving magnets 28 are positioned on an outer side of the side wall of the concave portion 21b. Accordingly, through magnetic attraction in a radial direction acting between the driven magnets 27 and the driving magnets 28, rotation of the rotor 26 is transmitted to the impeller 23. By rotation of the impeller 23, blood in the pump chamber 22 flows to be discharged from the outlet port. In accordance with this, blood is introduced from the inlet port 21a and thus blood flow is formed.
A blood pump is required not to cause thrombus formation, which is one of the specifications required for a blood pump. The presence of a structural member that obstructs a flow path in a blood pump causes blood stagnation and thereby is likely to induce thrombus formation. In the blood pump shown in FIG. 5, the upper bearing 24 is disposed in the inlet port 21a. The upper bearing 24 is positioned in the inlet port 21a that is comparatively narrow as a flow path, thereby considerably obstructing blood flow. Particularly, when a thick support 29 is provided so that the strength of a bearing portion is increased, the obstruction with respect to blood flow can be quite large.
In order to solve the aforementioned problem, an example is described in JP10(1998)-33664A that has a structure in which a shaft equipped with vanes of an impeller is made hollow so that a hollowed-out portion is used as a flow path. The outer periphery of the hollow shaft is supported by a magnetic bearing. This structure allows the hollowed-out portion to be free from a portion that obstructs blood flow. However, the hollow shaft is required to be relatively long and large in diameter, thereby being disadvantageous in making a device reduced in size and less complicated. For example, a blood pump for use with children has an inlet port with a diameter of about 6 mm. In this case, the structure described in JP10(1998)-33664A hardly can be adopted.
It also may be possible to solve the aforementioned problem by employing a structure in which an impeller is supported only by a bearing disposed in a lower portion of the impeller, so that an upper bearing is not required. However, supporting by a lower bearing alone is likely to cause instability of the rotation of an impeller. Particularly, in a structure in which rotation of a motor is transmitted to an impeller through magnetic coupling, it is desirable in terms of safety that the impeller be supported by two bearings disposed in upper and lower portions.
It is an object of the present invention to provide a turbo blood pump, in which an impeller is supported by upper and lower bearings, while obstruction to blood flow formed by the upper bearing is reduced, thereby being less likely to cause problems in terms of blood stagnation and thrombus formation.
The turbo blood pump of the present invention includes a housing having a pump chamber, an inlet port, and an outlet port, an impeller disposed rotatably in the pump chamber, upper and lower bearings supporting the impeller rotatably, and a driving force transmitting unit for driving the impeller to rotate. The upper bearing is supported at a position in the pump chamber below the inlet port, and the position is determined so that a cross-sectional area of the pump chamber in a plane including an upper end of the upper bearing and being orthogonal to a shaft of the impeller is larger than a cross-sectional area of a flow path of the inlet port at a portion where the inlet port is coupled to the pump chamber, and thus any obstruction to blood flow caused by disposing the upper bearing is of such a degree as to be permissible from the practical viewpoint.
According to this configuration, obstruction with respect to blood flow by an upper bearing is of such a degree as to be permissible, whereby a turbo blood pump is provided that is less likely to cause problems in terms of blood stagnation and thrombus formation.
In this configuration, preferably, the upper bearing is positioned in such a manner that a cross-sectional area SB of the pump chamber at a position of the upper end of the upper bearing satisfies the relationship, 2.32xc3x97SAxe2x89xa6SBxe2x89xa67.50xc3x97SA, with respect to a cross-sectional area SA of the inlet port at the portion where the inlet port is coupled to the pump chamber.
Furthermore, a configuration may be possible in which a plurality of bearing supports are fixed at a first end to a lower end of the inlet port and extend toward the pump chamber to support the upper bearing by a second end thereof.
Furthermore, the aforementioned configuration is effective in a turbo blood pump having a configuration in which the driving force transmitting unit includes driving magnets provided on a rotor disposed on an outer side of the housing, the rotor is rotatably driven by a motor, and driven magnets provided on the impeller, and the driven magnets and the driving magnets are opposed to each other with a wall of the housing being interposed between them to form a magnetic coupling for transmitting rotation of the rotor to the impeller.
In the case described above, a configuration may be possible in which the driven magnets and the driving magnets are disposed so that a direction of the magnetic coupling based on attraction acting between the driven magnets and the driving magnets is inclined with respect to a rotary shaft of the impeller.